Vicinal diols are useful as components in the production of polyesters and polyurethanes as well as in the cosmetic and pharmaceutical industry. They are produced, inter alia, by the saponification of their corresponding epoxides. This saponification may be catalyzed both by the addition of acids (c.f., for example, the state of the art of U.S. Pat. No. 3,576,890) and of alkalis (c.f., for example, DE-OS No. 17 93 247; DE-OS No. 22 03 806) and of salts of aliphatic mono or polycarboxylic acids (DE-OS No. 22 56 907) as well as primary, secondary or tertiary amine salts or ammonium salts (EP-OS 0 025 961).
It is also known that the acid, acting as catalyst, can be produced by means of the addition of esters of lower carboxylic acids which are hydrolyzed to alcohol and acids (U.S. Pat. No. 3,576,890). The saponification can be performed in a purely aqueous medium or in the presence of solubilizing agents such as water-soluble ketones or cyclic ethers (DE-OS No. 22 56 907). A purely aqueous saponification without the presence of organic solvents or solubilizing agents is more advantageous, since it avoids the step of separating the solvents or solubilizing agents after the saponification has been completed.
According to Houben-Weyl, vol. VI/3, 1964, pp. 454-455, saponifications which last several hours at temperatures far above 100.degree. C. and pressures of 12-20 bar are known which proceed without catalyst. In the presence of acid as catalyst, the saponification should proceed at "relatively low temperatures" and "rapidly"; more precise data is lacking.
However, according to a method described in "J. Am. Chem. Soc.", vol. 82, 1960, pp. 4328-29 (Korach) 2 hours are needed to produce cyclopentene diol by means of the saponification of epoxycyclopentene without the presence of a catalyst but in the presence of a solvent; the temperatures are set in two stages of 5.degree.-10.degree. C. at 15.degree.-20.degree. C. at an epoxide-water ratio of 1:12.
In the method of DE-AS 1 008 275, styrol oxide is saponified in the presence of an acidic catalyst such as sulfuric acid. However, the yields obtained are only approximately 80%.
DE-PS No. 34 42 938 teaches a continuous saponification of short chain epoxides in the presence of organic solvents with very good yields. This method includes the use of an organic solvent which is introduced e.g. from the epoxidation step of the epoxides used as starting materials.